1. Field of the Invention
The present invention relates to an airflow meter of a hot-wire type, particularly for measuring intake airflow of an internal combustion engine.
2. Description of the Related Art
in an intake airflow meter of hot-wire type, a resistor for measuring flow velocity and a resistor for temperature compensation are disposed with respect to an air passage, heating current is controlled so that, for example, the temperature of the resistor for measuring flow velocity is set under a condition at a specified temperature, and the airflow rate is calculated on the basis of the amount of this heating current.
Such an intake airflow meter for an internal combustion engine is disposed in an air intake pipe communicated with the internal combustion engine, the upstream side thereof having an air cleaner installed therein or the like and the downstream side thereof communicating with the internal combustion engine. Because of this structure, deviations in airflow from upstream and effects caused by backfiring of the internal combustion engine from downstream directly affect the resistor for measuring airflow velocity. Additionally, pulses corresponding to the combustion cycle of the revolving internal combustion engine exist in the airflow, making highly accurate, stabilized airflow measurement difficult.
However, when unclean air flows in from upstream of such an airflow meter, the measurement portion provided with the resistor for airflow measurement and the resistor for temperature compensation is soiled, and deterioration in measurement accuracy may be caused.